body{
    padding: 0;
    margin: 0;
}
.nav-bar{
    display: flex;
}
.nav-left, 
.nav-right{
height: 44px;
width: 70px;
line-height: 44px;
text-align: center;
background-color: red;
}
.nav-center{
    flex: 1;
    height: 44px;
    line-height: 44px;
text-align: center;
    background-color: blue;
}